Inductors that are commonly used in communication devices include core material around which one or more wires are coiled to form magnetic fields when current is applied. Typically, an inductor includes a core about which a wire is wound, and the wire terminates in two leads. The leads are inserted through holes in a printed circuit board to mount the inductor into a communication device. Leaded components, however, are undesirable in large volume manufacturing applications because each component must be manually disentangled from other components and pulled from a bin by a human operator. The component leads must then be manually straightened, adjusted at the correct distance from one another, and then threaded into the printed circuit board holes. Additionally, the component leads must be bent to secure the component during a wave soldering process, and excess wire must be trimmed from the leads. It can be seen that this process is time consuming and that over-handling and bending of the leads can result in breakage or deformation. Furthermore, if the wire leads are not stripped to the correct length, even proper assembly can result in poor mechanical and electrical coupling if, for example, the wire insulation extends through the printed circuit board hole to prevent the formation of adequate solder connections.
Alternatively, an inductor can be manufactured as a surface mount device, i.e., one that is mounted directly to the surface of a printed circuit board. To mount the inductor, it is placed on the surface of the board, which is moved through an oven in a solder reflow process. The temperatures of the oven are sufficiently high to liquefy solder placed between the inductor and the printed circuit board, and, once the board has cooled, the solder hardens to provide a mechanical and electrical connection between the inductor and the printed circuit board.
Some chip-type surface mount inductors are rectangular in shape. The wire surrounding the core is usually encapsulated in a plastic or other non-conductive material, and electrically conductive terminals at each end of the rectangular device are exposed for connection to a printed circuit board. Due to the rectangular shape, however, the magnetic field radiates outward, worsening the Q of the device and permitting flux leakage.
Toroidal inductors can be used to contain the magnetic field within the core, thereby preventing flux leakage and providing a better Q. One such device 100 is depicted in FIG. 1. As shown, the core 105 is toroidal, and a wire 110 is wound around the core 105. The wire 110 terminates in leads 115 that can be inserted into a printed circuit board for mounting.
Toroidal surface mount inductors can also be formed. These inductors are typically packaged in a non-conductive encapsulant material or housing. Electrically conductive device terminations are then provided on the exterior of the housing so that the device can be reflowed to a printed circuit board. Although the mounting process is simplified in this way, use of such an inductor can cause performance problems because the wire coils are not accessible for tuning. As a result, conventional surface mount toroidal inductors are only practical for use in devices in which a broad range of tolerances is acceptable. An additional consideration is that horizontally packaged toroidal inductors consume a large amount of space on a printed circuit board, and space considerations are of the utmost importance in consumer electronics, portable devices, and many other communication devices. Vertically mounted surface mount toroidal inductors, on the other hand, may lack mechanical integrity and can therefore be unreliable in portable devices or devices subject to vibration, temperature extremes, and other environmental conditions.
Thus, what is needed is a surface mount toroidal inductor that can be tuned for use in communication devices.